Lipoproteins, VLDLs and HDLs are synthesized by the hepatocyte for export into the serum. The secretory route they travel has been followed by morphology and cell fractionation studies. It appears that most of the intracellular lipoproteins are sequestered within the cisternal elements and vesicles of the Golgi apparatus. It is our goal to understand the Golgi phase of lipoprotein metabolism in the liver. Our experimental approach will be subcellular fractionation combined with biochemical and morphological characterization. First, well defined Golgi fractions will be isolated from rat liver. A control fractionation study will be undertaken to obtain Golgi fractions optimized for retention of lipoproteins within Golgi content as well as recovery of the Golgi marker enzyme, galactosyltransferase. An important corollary to this study will be a direct evaluation of the distribution of galactosyltransferase in situ and in isolation fraction by immunocytochemistry. Then by subfractionation, the Golgi content lipoproteins of density classes equivalent to serum lipoproteins will be isolated by flotation. Each density class will be characterized by morphology, and a balance sheet will be assembled on the lipid and protein components,. The nascent forms of the lipoproteins will be characterized, and the interactions (biosynthesis versus exchange) between the lipids of the Golgi membranes and Golgi content lipoproteins will be studied.